Method for producing a double-walled pipe and a double-walled pipe

ABSTRACT

The application relates to a method for producing a double-walled pipe ( 1 ) and a pipe ( 1 ) of this type, hating an outer pipe ( 3 ) which is press-fitted with an inner pipe ( 2 ) consisting of a corrosion-resistant alloy, wherein an adhesive ( 4 ) is inserted at least in regions between the outer pipe ( 3 ) and the inner pipe ( 2 ) wherein, after adhering the inner pipe ( 2 ) with the outer pipe ( 3 ), the inner pipe ( 2 ) and the adhesive layer ( 4 ) are removed at the pipe ends, and the inner side of the outer pipe ( 3 ) is plated via an integral connection with the inner pipe ( 2 ).

The invention relates to a method for producing a double-walled pipehaving an outer pipe that is pressed together with an inner pipepreferably made of a corrosion-resistant alloy, wherein an adhesive isintroduced at least in certain regions between the outer pipe and theinner pipe. The invention also relates to such a double-walled pipe.

DE 200 16 937 U1 discloses a bimetallic pipe that consists of a ferriticouter pipe into which is pressed, in an internal high-pressure formingmethod, an inner pipe made of a corrosion-resistant alloy, for examplestainless steel. The essential feature in the production of pipes ofthis kind is a hydraulic three-dimensional expansion process of an innerpipe in a seamless or welded outer pipe at ambient temperature. In theprocess, the inner pipe is first widened elastically and thenplastically between 2% and 5& until it bears against the internal wallof the outer pipe. This is followed by widening of the inner and outerpipes together, by approximately 0.5% to 1%, during which the outer pipeis held by a two-part outer tool. The mechano-hydraulic joining methodmakes it possible to join together a large number of differentmaterials, provided that the starting material meets the strengthcriteria.

In order to also use a bimetallic pipe for what is referred to as thereeling method, in which pipes are wound onto large reels and then drawnoff, generally in the context of laying offshore pipes, it is proposedthat an adhesive is provided at least in certain regions between theouter pipe and the inner pipe, in order to prevent the inner pipe or theliner detaching from the outer pipe or creasing during unrolling. Theadhesive is preferably a permanently elastic adhesive which canwithstand high tensile and shear forces. The adhesive can be applied inthe form of annular adhesive sleeves and then distributed evenly overthe lateral surface of the inner pipe before the latter is inserted intothe outer pipe. In order to ensure defect-free welding of bimetallicpipes to form a pipeline, it is expedient if the two pipe ends of eachbimetallic pipe are free from adhesive. The end faces of the pipesshould also be free from adhesive.

The present invention has the object of providing a method that permitssimple production of double-walled, reelable pipes. The invention hasthe further object of providing an improved, double-walled, reelablepipe.

According to the invention, this object is achieved with a method havingthe features of the main claim and a double-walled pipe having thefeatures of the further independent claim. Advantageous configurationsand refinements of the invention are disclosed in the dependent claims,the description and the figures.

The inventive method for producing a double-walled pipe having an outerpipe that is pressed together with an inner pipe preferably made of acorrosion-resistant alloy, wherein an adhesive is introduced at least incertain regions between the outer pipe and the inner pipe, providesthat, after adhesive bonding of the inner pipe to the outer pipe, theinner pipe and the adhesive layer are. removed at the pipe ends, and theinside of the outer pipe is plated forming a material-bonded connectionwith the inner pipe. The inner pipe is pressed into the outer pipe bywidening from within; alternatively or in addition pressing is achievedby pressing the outer pipe together or by reducing the internal diameterof the outer pipe, for example by cooling or by reducing an internalpressure after widening of the outer pipe. Removing part of the innerpipe and the adhesive layer permits high-quality application of theweld-plating to the inside of the outer pipe so as to also be able tosatisfy the safety requirements for weld-plating or for a double-walledpipe. If weld-plating is carried out with the presence of adhesive oradhesive residue, there is the risk of inclusions, voids or poresforming within the weld-plated layer, which can impair the durabilityand quality and possibly also the required stability of the pipe. Thematerial-bonded connection of the weld-plating with the outer pipe andwith the inner pipe makes it possible to provide a mechanically stablepipe end which can easily be connected to a corresponding double-walledpipe by welding at the end faces, making it possible to produce long,reelable pipes consisting of the double-walled pipe sections. Theadhesive layer effectively avoids creasing of the inner pipe or linerduring rolling and unrolling of the pipe strand onto and from the pipereel, so that on one hand there is nothing to impede the flow and on theother hand there is no danger of corrosion in the interspace between thefold of the inner pipe and the outer pipe.

Weld-plating of the inside of the pipe ends of the outer pipe protectsthe outer pipe against wear, oxidation and corrosion. The weld-platingconnects the different materials of the inner pipe and of the outer pipein a material-bonded manner, the material that is weld-plated to theinside of the outer pipe being more highly alloyed than the material ofthe outer pipe.

The pipe ends of the inner pipe can be removed thermally and/ormechanically in order to gain access to the adhesive layer that islocated in the region of the pipe ends, between the inner pipe and theouter pipe, or in order to gain access to the outer pipe, after removalof the pipe ends of the inner pipe, over the length destined forapplication of the weld-plating. In the region of the pipe end that isto be separated, the inner pipe can be separated mechanically, forexample by lathing, milling or grinding, but also by thermal methodssuch as laser beam cutting, laser beam oxygen cutting or thermalcutting. Alternatively or in addition, use is made of abrasive or othermaterial-removing separating methods in which the inner pipe by physicaland chemical active. principles in the form of electrical energy,thermal energy, chemical reactions and combinations thereof used forcutting. The pipe ends can be removed entirely thermally and/ormechanically, or it is alternatively possible to remove just a slit oran annular part of the inner pipe and then remove the separated part ofthe inner pipe, which is held only by the adhesive layer, from the outerpipe. Removing the inner pipe section that is to be removed is performedfor example by the application of tensile forces or compressive forcesor by the application of torsional forces, in order to break the hold ofthe adhesive. It is also possible, after the mechanical and/or thermalseparation or parting of the pipe end of the inner pipe that is to beremoved, to remove the adhesive layer chemically, electro-chemically,thermally or mechanically, or to reduce or destroy the adhesive force ofthe adhesive to the point that the separated inner pipe end can beremoved from the outer pipe.

After removal of the inner pipe end, any adhesive remaining in theregion of the pipe ends on the inside of the outer pipe can be removedthermally, chemically and/or mechanically, for example by heating,combustion, chemical dissolution or conversion or by mechanicalfinishing methods. It is also possible to remove adhesive from a regionbetween the inner pipe and the outer pipe, after removal of an innerpipe end, so as to obtain an adhesive-free gap between the inner pipeand the outer pipe.

The surface of the inside of the outer pipe can be chemically and/ormechanically processed prior to plating, in order to ensure improvedadhesion between the plated-on material and the outer pipe. Inparticular, residues of adhesives and possibly of the materials used forremoving the adhesives are removed by machining the inside of the outerpipe. Thus, the surface is cleaned and possibly prepared by surfacetreatment such that optimal plating can take place.

During production of the double-walled pipe, the inner pipe is firstadhesively bonded over the entire length such that two essentiallyequal-length pipe sections of the inner pipe and the: outer pipe:produce a double-walled pipe as an intermediate product, the pipes beingadhesively bonded to one another over the entire length andadvantageously also over their entire surface area. This simplifies theapplication of the adhesive since errors in guiding the pipes duringinsertion of the inner pipe into the outer pipe are unproblematic as noregions of the inner pipe or Of the outer pipe should be excluded fromapplication of adhesive. The full-surface area adhesive bonding of theinner pipe to the outer pipe produces a reliable arrangement of theinner pipe with respect to the outer pipe and prevents creasing of theinner pipe Cr liner during reeling.

The inner pipe is advantageously made of a corrosion-resistant alloy, inparticular a chromium-nickel steel or a nickel-based alloy, the outerpipe preferably being a pipe made of a carbon steel. The weld-platingconnects the different types of steel to one another in amaterial-bonded manner.

The adhesive used is preferably a permanently elastic adhesive in orderto be able to compensate for differences in thermal expansion orpossibly relative movement between the inner pipe and the outer pipeduring loading and laying.

The inner pipe and/or the outer pipe can be cooled during plating. Bymeans of the weld-plating, which is advantageously carried out in acircumferential welding process in which during the welding process thepipe is rotated relative to the plated-on material or a welding torch oran electrode, first of all the truncated inner pipe is connected to theouter pipe in a material-bonded manner by the weld-plating material.Starting at this region inside the outer pipe, more material is thendeposited in a helical shape in the direction of the pipe end until theweld-plating extends, on the inside of the outer pipe, from thetruncated inner pipe to the pipe end at the end face. In order to avoidexcessive temperature peaks that might reduce the adhesive strength ofthe adhesive, localized cooling acting on the pipes from inside or fromoutside is advantageous. Cooling can start prior to beginning theweld-plating. During weld-plating, cooling can be provided both frominside and from outside, and it is also possible to cool just from oneside. Subsequent cooling can also take place.

The weld-plating material forms a closed sheath over the inside of theouter pipe and covers the inside of the latter, wherein the materialused for plating is also corrosion-resistant.

The double-walled pipe having an outer pipe that is pressed togetherwith an inner pipe, preferably the inner pipe is pressed into the outerpipe, wherein an adhesive is arranged at least in certain regionsbetween the outer pipe and the inner pipe, provides that a weld-platingthat connects the outer pipe to the inner pipe in a material-bondedmanner is applied at the pipe ends of the outer pipe. Thus, the innerpipe is truncated compared to the outer pipe, this corresponding to thelength of the weld-plating by means of which the inner pipe is coupledto the outer pipe in a material-bonded manner, wherein the weld-platingis preferably applied to the full surface area of the inside of theouter pipe in order to protect the outer pipe from mechanical andchemical effects. The inner pipe is preferably made of acorrosion-resistant alloy, in particular a chromium-nickel steel or anickel-based alloy, while the outer pipe is preferably made of a carbonsteel.

The weld-plating is preferably applied to the outer pipe over a lengthof 50 mm to 250 mm as seen from the pipe end, in order to provide, overa sufficient length, a wholly metallic end face of the double-walledpipe so that two end faces of mutually opposite double-walled pipes canreadily be welded to one another. The length of the weld-plating meansthat the pipe ends or the end faces can be mechanically pre-machined inorder to permit reliable and automatable welding of pipe ends to producea long pipe strand.

The weld-plating preferably extends as far as the end of the outer pipe,so that the inside of the outer pipe is fully protected againstcorrosion, namely first by the weld-plating and then, over the remaininglength of the pipe, by the inner pipe or liner.

The internal diameter of the weld-plating preferably corresponds to theinternal diameter of the inner pipe, which ensures that no vortices orflow obstructions arise in the double-walled pipe, and a double-walledpipe of near-constant internal diameter can be provided even when pipeends are welded to one another.

There follows a more detailed explanation of an exemplary embodiment ofthe invention, with reference to the appended drawings, in which:

FIG. 1 is a view in section of a double-walled pipe end after adhesivebonding;

FIG. 2 is a perspective partial view in section of the pipe end of FIG.1;

FIG. 3 is a view in section of a pipe end after removal of an inner pipepart and during weld-plating; and

FIG. 4 is a perspective partial view in section of FIG. 3.

FIG. 1 shows, in a partial view in section, one end of a double-walledpipe 1 having an inner pipe 2 that is adhesively bonded to an outer pipe3 by means of an adhesive layer 4 applied to the full surface area. Theouter pipe 3 is made of a carbon steel and is substantially thicker thanthe inner pipe 2, which is designed as what is referred to as a linerand is made of a corrosion-resistant material, preferably achromium-nickel steel or a nickel-based alloy. In order to produce thedouble-walled pipe 1, the entire surface area and the entire length ofthe outside of the inner pipe 2, or the inside of the outer pipe 3, isprovided with the adhesive 4. In the non-assembled state, the externaldiameter of the inner pipe 2 is smaller than the internal diameter ofthe outer pipe 3. After insertion of the inner pipe 2 into the outerpipe 3, the inner pipe 2 is widened mechanically, for examplehydro-mechanically, such that the outside of the inner pipe 2 comes intocontact with the adhesive 4 and together at least slightly widens theouter pipe 3. Alternatively or in combination, the inner pipe 2 can beinserted into a widened outer pipe 3 whose internal diameter is thenreduced, for example by relaxation, compression of the outer pipe orcooling. At the end of the mechanical plating procedure, the inner pipe2 bears evenly against the inside of the outer pipe 3 and is stronglybonded thereto by means of the adhesive layer 4. In addition, the innerpipe 2 is positioned and fixed in the outer pipe 3 by means of themechanical clamping owing to the different return paths of the innerpipe 2 and the outer pipe 3 due to the mechanical widening orcompression.

Both FIG. 1 and FIG. 2 show that the adhesive layer is applied evenlyover the entire circumference of the inner pipe 2 and the internalcircumference of the outer pipe 3, the adhesive layer 4 extends up tothe end face of the double-walled pipe 1, and thus the inner pipe end 21is also connected to the outer pipe end 31 by the adhesive layer 4. Thefurther processing of the double-walled pipe 1 proceeds from this state.

FIGS. 3 and 4 show a pipe end of a double walled pipe 1 at the end ofits completion. One part of the inner pipe end 21 has been removed, forexample by lathing, milling or grinding the inner pipe end 21.Alternative methods for removing the inner pipe end 21 can includemaking a circumferential slit and pulling out the separated pipe end,possibly after removal or deactivation of the adhesive layer 4 in thatregion. The circumferential slit can be created by mechanical removal orparting methods, but also by thermal parting methods such as thermalcutting, laser oxygen cutting or electro-chemical or chemical processes.After removal of the inner pipe end 21, any remaining adhesive layer 4is fully removed. This removal can be carried out thermally,mechanically, chemically or using a combination of several of thesemethods. It is also possible and provided that the surface of the insideof the outer pipe end 31, which is free from the adhesive layer 4, ismechanically machined, for example ground or polished. This is followedby depositing a weld-plating 5, using a welding torch 6, onto that partof the double-walled pipe 1 from which the inner pipe end 21 has beenremoved. The deposition of the weld-plating 5 can be performed in acircumferential deposition process in which either the double-walledpipe 2, or the welding torch 6 together with the welding material thatis to be deposited, is rotated. The weld-plating 5 extends up to thepipe end, that is to say up to the end face of the outer pipe 3, andconnects the outer pipe 3 to the inner pipe 2 in a material-bondedmanner. In the process, the adhesive layer 4 preferably reaches up tojust before the weld-plating 5. In order to avoid thermal damage in theweld zone, the outer pipe 3 and/or the inner pipe 2 can be cooled, inparticular locally cooled, during weld-plating.

The internal diameter of the weld-plating 5 corresponds to the internaldiameter of the inner pipe 2, it still being possible for theweld-plating 5 to be mechanically machined after the deposition weldingin order to achieve an essentially smooth-walled surface of theweld-plating 5. After completion of the weld-plating 5, the end face ofthe outer pipe end 31 is entirely metallic, the weld-plating can extendinto the double-walled pipe 1 over a length of 50 mm to 250 mm from theend face of the outer pipe 3.

1. A method for producing a double-walled pipe having an outer pipe thatis pressed together with an inner pipe made of a corrosion-resistantalloy, comprising: wherein an introducing an adhesive at least incertain regions between the outer pipe (3) and the inner pipe foradhesive bonding of the inner pipe to the outer pipe; removing the innerpipe at pipe ends of the inner pipe and removing an adhesive layer ofthe adhesive at the pipe ends of the outer pipe; and plating an insideof the outer pipe to form material-bonded connection with the innerpipe.
 2. The method as claimed in claim 1, wherein the pipe ends of theouter pipe are weld-plated on the inside.
 3. The method as claimed inclaim 1, further comprising removing the pipe ends of the inner pipethermally and/or mechanically.
 4. The method as claimed in claim 1,further comprising removing a portion of the adhesive in a region of thepipe ends on the inside of the outer pipe and/or between the inner pipeand the outer pipe, wherein removing is performed thermally and/ormechanically.
 5. The method as claimed in claim 1 wherein a surface ofthe inside of the outer pipe is chemically and/or mechanically processedprior to plating.
 6. The method as claimed in claim 1 wherein the innerpipe is adhesively bonded over an entire length of the inner pipe. 7.The method as claimed in claim 1 wherein the inner pipe is adhesivelybonded over an entire surface area of the inner pipe.
 8. The method asclaimed in claim 1 further comprising cooling during plating the innerpipe and/or the outer pipe.
 9. A double-walled pipe, comprising: anouter pipe that is pressed together with an inner pipe; an adhesivearranged at least in certain regions between the outer pipe and theinner pipe; and a weld-plating that connects the outer pipe to the innerpipe in a material-bonded manner, wherein the weld-plating is applied atpipe ends of the outer pipe.
 10. The double-walled pipe as claimed inclaim 9 wherein the inner pipe is made of a corrosion-resistant alloy,and wherein the outer pipe is made of a carbon steel.
 11. Thedouble-walled pipe as claimed in claim 9 wherein the weld-plating islocated on the outer pipe over a length of 50 mm to 250 mm at a pipeend.
 12. The double-walled pipe as claimed in claim 9 wherein theweld-plating extends as far as an end face of the outer pipe.
 13. Thedouble-walled pipe as claimed in claim 9 wherein an internal diameter ofthe weld-plating corresponds to an internal diameter of the inner pipe.14. The double-walled pipe as claimed in claim 10 wherein thecorrosion-resistant alloy is selected from the group consisting ofchromium-nickel steel and nickel-based alloy.